DESCRIPTION (Verbatim from the Applicant's Abstract): G protein mediated signal transduction is a fundamental mechanism of cell communication. A variety of neurotransmitters and hormones transduce signals mediated through G proteins to induce various physiological responses. G proteins are highly expressed in brain. However their physiological function in brain is poorly characterized. The objective of this study is to understand the molecular mechanism and physiological function of G protein-mediated signaling pathways in brain. Among G proteins, Gao is highly expressed in brain. We recently identified novel candidate targets for Gao, GRIN I and GRIN2 by cDNA expression cloning strategy using phosphorylated Ga subunit as a probe. GRINI and GRIN2 are specifically expressed in brain and stimulate neurite growth when coexpressed with constitutively active mutant of Gao. In this proposal, we will investigate the molecular mechanism of the regulation of neurite growth through Gao-GRIN 1 or GRIN2 pathways in detail. We will analyze the biochemical mechanism of Gao-GRIN pathway to induce neurite growth. We will attempt to understand functional domains of GRIN 1 and GRIN2 and characterize their down stream components. We will also try to understand the role of this pathway in primary cultured neurons. In addition, we will analyze the function of GRIN1 or GRIN2 in vivo by generating transgenic mice or gene-knockout mice for GRIN1 or GRIN2. We will also investigate the mechanism of regulation of this pathway by receptor activation, RGS proteins, or by other G protein-mediated pathway.